This invention relates to a color separation and additive color mixing system for photographic, cinematographic and/or telecommunication equipment, with means for intensity control of the various color channels, and with means for black and white storage of the color information in each color channel.
In one embodiment of the invention, the system can be used to store color and contour picture information contained in a single multi-color light beam on several black and white film media. For this purpose the light beam, comprising color and contour information of a colored picture, is split into several mono-color beams of selected color band, e.g., in three beams having the three basic colors red, green and blue, respectively. The mono-color beams are individually intensity corrected by light modulators without losing any of their contour information. After these intensity corrections, the contour information and the overall mono-color intensity information of the mono-color beams can be stored on black and white film media. With this technique, it becomes possible to store multi-color pictures from either color films, color transparencies, or from directly projected images from natural surroundings on black and white film which is much cheaper than color film. Any suitable black and white film can be used, including those that do not require silver, these films being much less expensive than presently available color films.
The same system can be used to reproduce color pictures from black and white film media, each color of the picture being stored on respective black and white film pictures, according to the number of color channels used in the storage process. The different film media which contain each contour and mono-color intensity information of a stored multi-color picture are respectively positioned in a mono-color light beam which is produced by splitting a multi-color light beam into mono-color light beams of the same color band as the light beams which were used for production of the black and white film media. After modulation by the films, the mono-color light beams will contain the correct contour and intensity information of the picture to be projected. Here again, intensity can be corrected by light modulators in the mono-color beams and a resulting multi-color beam produced by additively mixing the mono-color beams will reproduce the stored multi-color picture with corrected color components.
The novel system of the invention is also useful for film copying techniques, copying one color film from another, the color composition of the former being corrected in each color channel. Splitting of the image into color channels and recombining the mono-color channels can be performed in one step without intermediate storing on black and white film media or on mono-color film media.
Known devices for controlling light intensity include mechanical shutters, sometimes called light modulators. The shutters may be mechanically controlled by double flaps moved by a servo-motor. These techniques are disadvantageous in that the switching time for changing the light amplitude between 0 and 100% is relatively long, typically about 2 .times. 10.sup.-3 seconds. Owing to this disadvantage, it is practically impossible, in film copying techniques, to exceed printing speeds of about 3000 m/h. For high quality prints, the maximum speed now used is as low as 2000 m/h.
A second disadvantage of the above-mentioned mechanical shutters is that they switch over with residual oscillations or bounce, which results in significant color flicker, lowering the quality of color pictures.
A third significant disadvantage is that mechanical shutters do not permit infinite variation of the intensity of a modulated beam. Moreover, since intensity modulation is always performed by changing aperture cross-section, the picture periphery will be damaged without additional optics.
In another known light-intensity control device, a number of filters, for instance eight filters, are shot into a magazine filled with silicone oil by compressed air. This system is of the mechanical type and also has the first two disadvantages mentioned above for the shutter.
It is one object of the present invention to provide an overall color correction system which has a substantially shorter switching time for intensity control and better color separation between the various color channels, so that color pictures of higher quality can finally be obtained than was heretofore possible.
Another object of this invention is to provide an inexpensive method and apparatus for storage of color images on black and white film.
The arrangement of the present invention allows substantial reduction of the switchover time for intensity level variations. Thus, the invention provides a system which comprises anti-reflex coated dichroic filter glasses for the purpose of color separation, and further comprises controlled electro-optical or magneto-optical cells for intensity control of the various color channels and which permit short-time control of the color channels in such a manner that intensity control with respect to the color channels takes place without overlapping and without any residual oscillation. This arrangement substantially reduces the switching time for impulse control.
The switching time from a maximum transparency to a minimum may be shorter than 10.sup.-5 seconds. With this improvement, it is possible to make film copying machines which are able to process film at a speed of about 30,000 m/h.
As compared to the mechanical behavior of mechanical shutters, electric switching behavior of the modulators' control elements can be varied, and the switching behavior exactly predicted and modified. The use of electro-optic or magneto-optic light modulators ensures that the change from one transparency level to another can be optimally fitted to individual needs. By enlarging the rising or falling times in switching from one level to another according to correction values of subsequent pictures, one can smooth the switch-over from one picture to the next. As the switching behavior of electric circuits (step response) is given by their damping factors, the influence of one switching cycle to the next can be influenced by changing this factor, so that step response of the circuit will reach a "low" value only to a selectable amount before the next positive switching step is applied. If the step response reaches a "low" value before the next positive switching step is applied, overlapping can completely be omitted.